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-rw-r--r--src/mesa/drivers/dri/i965/brw_lower_texture_gradients.cpp201
1 files changed, 182 insertions, 19 deletions
diff --git a/src/mesa/drivers/dri/i965/brw_lower_texture_gradients.cpp b/src/mesa/drivers/dri/i965/brw_lower_texture_gradients.cpp
index 7a5f9834423..d571ecd4394 100644
--- a/src/mesa/drivers/dri/i965/brw_lower_texture_gradients.cpp
+++ b/src/mesa/drivers/dri/i965/brw_lower_texture_gradients.cpp
@@ -48,6 +48,7 @@ public:
private:
void emit(ir_variable *, ir_rvalue *);
+ ir_variable *temp(void *ctx, const glsl_type *type, const char *name);
};
/**
@@ -60,6 +61,17 @@ lower_texture_grad_visitor::emit(ir_variable *var, ir_rvalue *value)
base_ir->insert_before(assign(var, value));
}
+/**
+ * Emit a temporary variable declaration
+ */
+ir_variable *
+lower_texture_grad_visitor::temp(void *ctx, const glsl_type *type, const char *name)
+{
+ ir_variable *var = new(ctx) ir_variable(type, name, ir_var_temporary);
+ base_ir->insert_before(var);
+ return var;
+}
+
static const glsl_type *
txs_type(const glsl_type *type)
{
@@ -144,28 +156,179 @@ lower_texture_grad_visitor::visit_leave(ir_texture *ir)
new(mem_ctx) ir_variable(grad_type, "dPdy", ir_var_temporary);
emit(dPdy, mul(size, ir->lod_info.grad.dPdy));
- /* Calculate rho from equation 3.20 of the GL 3.0 specification. */
- ir_rvalue *rho;
- if (dPdx->type->is_scalar()) {
- rho = expr(ir_binop_max, expr(ir_unop_abs, dPdx),
- expr(ir_unop_abs, dPdy));
- } else {
- rho = expr(ir_binop_max, expr(ir_unop_sqrt, dot(dPdx, dPdx)),
- expr(ir_unop_sqrt, dot(dPdy, dPdy)));
- }
-
- /* lambda_base = log2(rho). We're ignoring GL state biases for now.
- *
- * For cube maps the result of these formulas is giving us a value of rho
- * that is twice the value we should use, so divide it by 2 or,
- * alternatively, remove one unit from the result of the log2 computation.
- */
ir->op = ir_txl;
if (ir->sampler->type->sampler_dimensionality == GLSL_SAMPLER_DIM_CUBE) {
- ir->lod_info.lod = expr(ir_binop_add,
- expr(ir_unop_log2, rho),
- new(mem_ctx) ir_constant(-1.0f));
+ /* Cubemap texture lookups first generate a texture coordinate normalized
+ * to [-1, 1] on the appropiate face. The appropiate face is determined
+ * by which component has largest magnitude and its sign. The texture
+ * coordinate is the quotient of the remaining texture coordinates against
+ * that absolute value of the component of largest magnitude. This
+ * division requires that the computing of the derivative of the texel
+ * coordinate must use the quotient rule. The high level GLSL code is as
+ * follows:
+ *
+ * Step 1: selection
+ *
+ * vec3 abs_p, Q, dQdx, dQdy;
+ * abs_p = abs(ir->coordinate);
+ * if (abs_p.x >= max(abs_p.y, abs_p.z)) {
+ * Q = ir->coordinate.yzx;
+ * dQdx = ir->lod_info.grad.dPdx.yzx;
+ * dQdy = ir->lod_info.grad.dPdy.yzx;
+ * }
+ * if (abs_p.y >= max(abs_p.x, abs_p.z)) {
+ * Q = ir->coordinate.xzy;
+ * dQdx = ir->lod_info.grad.dPdx.xzy;
+ * dQdy = ir->lod_info.grad.dPdy.xzy;
+ * }
+ * if (abs_p.z >= max(abs_p.x, abs_p.y)) {
+ * Q = ir->coordinate;
+ * dQdx = ir->lod_info.grad.dPdx;
+ * dQdy = ir->lod_info.grad.dPdy;
+ * }
+ *
+ * Step 2: use quotient rule to compute derivative. The normalized to
+ * [-1, 1] texel coordinate is given by Q.xy / (sign(Q.z) * Q.z). We are
+ * only concerned with the magnitudes of the derivatives whose values are
+ * not affected by the sign. We drop the sign from the computation.
+ *
+ * vec2 dx, dy;
+ * float recip;
+ *
+ * recip = 1.0 / Q.z;
+ * dx = recip * ( dQdx.xy - Q.xy * (dQdx.z * recip) );
+ * dy = recip * ( dQdy.xy - Q.xy * (dQdy.z * recip) );
+ *
+ * Step 3: compute LOD. At this point we have the derivatives of the
+ * texture coordinates normalized to [-1,1]. We take the LOD to be
+ * result = log2(max(sqrt(dot(dx, dx)), sqrt(dy, dy)) * 0.5 * L)
+ * = -1.0 + log2(max(sqrt(dot(dx, dx)), sqrt(dy, dy)) * L)
+ * = -1.0 + log2(sqrt(max(dot(dx, dx), dot(dy,dy))) * L)
+ * = -1.0 + log2(sqrt(L * L * max(dot(dx, dx), dot(dy,dy))))
+ * = -1.0 + 0.5 * log2(L * L * max(dot(dx, dx), dot(dy,dy)))
+ * where L is the dimension of the cubemap. The code is:
+ *
+ * float M, result;
+ * M = max(dot(dx, dx), dot(dy, dy));
+ * L = textureSize(sampler, 0).x;
+ * result = -1.0 + 0.5 * log2(L * L * M);
+ */
+
+/* Helpers to make code more human readable. */
+#define EMIT(instr) base_ir->insert_before(instr)
+#define THEN(irif, instr) irif->then_instructions.push_tail(instr)
+#define CLONE(x) x->clone(mem_ctx, NULL)
+
+ ir_variable *abs_p = temp(mem_ctx, glsl_type::vec3_type, "abs_p");
+
+ EMIT(assign(abs_p, swizzle_for_size(abs(CLONE(ir->coordinate)), 3)));
+
+ ir_variable *Q = temp(mem_ctx, glsl_type::vec3_type, "Q");
+ ir_variable *dQdx = temp(mem_ctx, glsl_type::vec3_type, "dQdx");
+ ir_variable *dQdy = temp(mem_ctx, glsl_type::vec3_type, "dQdy");
+
+ /* unmodified dPdx, dPdy values */
+ ir_rvalue *dPdx = ir->lod_info.grad.dPdx;
+ ir_rvalue *dPdy = ir->lod_info.grad.dPdy;
+
+ /* 1. compute selector */
+
+ /* if (abs_p.x >= max(abs_p.y, abs_p.z)) ... */
+ ir_if *branch_x =
+ new(mem_ctx) ir_if(gequal(swizzle_x(abs_p),
+ max2(swizzle_y(abs_p), swizzle_z(abs_p))));
+
+ /* Q = p.yzx;
+ * dQdx = dPdx.yzx;
+ * dQdy = dPdy.yzx;
+ */
+ int yzx = MAKE_SWIZZLE4(SWIZZLE_Y, SWIZZLE_Z, SWIZZLE_X, 0);
+ THEN(branch_x, assign(Q, swizzle(CLONE(ir->coordinate), yzx, 3)));
+ THEN(branch_x, assign(dQdx, swizzle(CLONE(dPdx), yzx, 3)));
+ THEN(branch_x, assign(dQdy, swizzle(CLONE(dPdy), yzx, 3)));
+ EMIT(branch_x);
+
+ /* if (abs_p.y >= max(abs_p.x, abs_p.z)) */
+ ir_if *branch_y =
+ new(mem_ctx) ir_if(gequal(swizzle_y(abs_p),
+ max2(swizzle_x(abs_p), swizzle_z(abs_p))));
+
+ /* Q = p.xzy;
+ * dQdx = dPdx.xzy;
+ * dQdy = dPdy.xzy;
+ */
+ int xzy = MAKE_SWIZZLE4(SWIZZLE_X, SWIZZLE_Z, SWIZZLE_Y, 0);
+ THEN(branch_y, assign(Q, swizzle(CLONE(ir->coordinate), xzy, 3)));
+ THEN(branch_y, assign(dQdx, swizzle(CLONE(dPdx), xzy, 3)));
+ THEN(branch_y, assign(dQdy, swizzle(CLONE(dPdy), xzy, 3)));
+ EMIT(branch_y);
+
+ /* if (abs_p.z >= max(abs_p.x, abs_p.y)) */
+ ir_if *branch_z =
+ new(mem_ctx) ir_if(gequal(swizzle_z(abs_p),
+ max2(swizzle_x(abs_p), swizzle_y(abs_p))));
+
+ /* Q = p;
+ * dQdx = dPdx;
+ * dQdy = dPdy;
+ */
+ THEN(branch_z, assign(Q, swizzle_for_size(CLONE(ir->coordinate), 3)));
+ THEN(branch_z, assign(dQdx, CLONE(dPdx)));
+ THEN(branch_z, assign(dQdy, CLONE(dPdy)));
+ EMIT(branch_z);
+
+ /* 2. quotient rule */
+ ir_variable *recip = temp(mem_ctx, glsl_type::float_type, "recip");
+ EMIT(assign(recip, div(new(mem_ctx) ir_constant(1.0f), swizzle_z(Q))));
+
+ ir_variable *dx = temp(mem_ctx, glsl_type::vec2_type, "dx");
+ ir_variable *dy = temp(mem_ctx, glsl_type::vec2_type, "dy");
+
+ /* tmp = Q.xy * recip;
+ * dx = recip * ( dQdx.xy - (tmp * dQdx.z) );
+ * dy = recip * ( dQdy.xy - (tmp * dQdy.z) );
+ */
+ ir_variable *tmp = temp(mem_ctx, glsl_type::vec2_type, "tmp");
+ EMIT(assign(tmp, mul(swizzle_xy(Q), recip)));
+ EMIT(assign(dx, mul(recip, sub(swizzle_xy(dQdx),
+ mul(tmp, swizzle_z(dQdx))))));
+ EMIT(assign(dy, mul(recip, sub(swizzle_xy(dQdy),
+ mul(tmp, swizzle_z(dQdy))))));
+
+ /* M = max(dot(dx, dx), dot(dy, dy)); */
+ ir_variable *M = temp(mem_ctx, glsl_type::float_type, "M");
+ EMIT(assign(M, max2(dot(dx, dx), dot(dy, dy))));
+
+ /* size has textureSize() of LOD 0 */
+ ir_variable *L = temp(mem_ctx, glsl_type::float_type, "L");
+ EMIT(assign(L, swizzle_x(size)));
+
+ ir_variable *result = temp(mem_ctx, glsl_type::float_type, "result");
+
+ /* result = -1.0 + 0.5 * log2(L * L * M); */
+ EMIT(assign(result,
+ add(new(mem_ctx)ir_constant(-1.0f),
+ mul(new(mem_ctx)ir_constant(0.5f),
+ expr(ir_unop_log2, mul(mul(L, L), M))))));
+
+ /* 3. final assignment of parameters to textureLod call */
+ ir->lod_info.lod = new (mem_ctx) ir_dereference_variable(result);
+
+#undef THEN
+#undef EMIT
+
} else {
+ /* Calculate rho from equation 3.20 of the GL 3.0 specification. */
+ ir_rvalue *rho;
+ if (dPdx->type->is_scalar()) {
+ rho = expr(ir_binop_max, expr(ir_unop_abs, dPdx),
+ expr(ir_unop_abs, dPdy));
+ } else {
+ rho = expr(ir_binop_max, expr(ir_unop_sqrt, dot(dPdx, dPdx)),
+ expr(ir_unop_sqrt, dot(dPdy, dPdy)));
+ }
+
+ /* lambda_base = log2(rho). We're ignoring GL state biases for now. */
ir->lod_info.lod = expr(ir_unop_log2, rho);
}
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